Effect of grain morphology and grain size on the mechanical properties of Al2O3 ceramics

Bending strength, fracture toughness, fracture energy and crack extension resistance were evaluated for Al₂O₃ ceramics with equi-axed and platelet grains. Bending strength was proportional to grain size^–1/2, but flaws with a size of 10 m controlled the strength when the microstructure was finer than 10 m. Fracture toughness, measured by the single etched precracked beam (SERB) method, was proportional to fracture energy^1/2, and increased with the grain size of Al₂O₃ ceramics with equi-axed and platelet grains. However, the toughness of platelet grain ceramics was higher than the ceramics with equi-axed grains, and increased up to 6.6 MPam^1/2 with grain size. Therefore, it is thought that fracture toughness not only depends on grain size, but also on grain morphology; equations were derived to account for this phenomenon.     

Ion-plated thick films of Al2O3 on stainless steels and Inconel

Gasless ion-plated films of Al₂O₃ and various alloys which served as adhesion layers were evaluated for thermal cycling stability and abrasion resistance. Substrates included Inconel and 304, 310 and 316 stainless steel test plaques. Work was extended to include the coating of the internal surface of Inconel cylinders. Both resistance-heated (tungsten baskets) and induction-heated (I-Gun^tm ion source) sources were used with combination r.f. and d.c. biasing.     

Luminescent and scintillation properties of Lu3Al5O12:Sc single crystal and single crystalline films

The work is dedicated to growth by the liquid phase epitaxy method and study of the luminescence and scintillation properties of Sc³⁺ doped single crystalline films (SCF) of Lu₃Al₅O₁₂ (LuAG) garnet. The scintillation properties of SCF are compared with single crystal (SC) analogues grown by the Horizontal Direct Crystallization and Czochralski methods. We consider the dependence of intensity of the Sc³⁺ emission in LuAG host on the activator concentration and influence of flux contamination on the light yield (LY) of the Sc³⁺ luminescence in LuAG:Sc SCF with respect to their SC counterparts and the reference YAP:Ce scintillator. From the NMR investigations of LuAG:Sc SCF we confirm the substitution by Sc³⁺ ions both the octahedral and dodecahedral positions of LuAG host and formation of the Sc_Al and Sc_Lu related emission centers, respectively. We also show that the luminescence spectrum in the UV range and decay kinetics of LuAG:Sc SCF can be effectively tuned by changing the scandium content.     

Characterization of Al2O3 films deposited by various methods

A comparative study of electron emission characteristics was made for thin films of Al₂O₃ deposited by the techniques of r.f. sputtering, chemical vapour desposition and post-oxidation of vacuum-evaporated aluminum films. A single pusle method was used with a retarding field analyzer for measurement of the yield in secondary electron emission. Relative work functions were determined with respect to gold by a diode gun assembly and the retarding potential method. All measurements were made in an ultrahigh vacuum system. X-ray photoelectron spectroscopy and scanning electron microscopy were used for comparison of the stoichiometry and morphology of the films, and the relative effects of these characteristics on the emission were assessed.The emission characteristics were analyzed semi-empirically by making use of Dionne's theory for secondary electron emission. On the basis of the experimental results, the use of these films in continuing dynodes (for electron multipliers) is proposed. The r.f. sputtered films were found to be the most suitable electron emissive layers.     

Hardness and grain size relations for thick chromium films deposited by hallow cathode discharge

Chromium films deposited by hollow cathode discharge show a variety of hardness, wear resistance and anti-corrosion characteristics. To find the relation between these properties and the film structure, investigations using X-ray diffraction, transmission electron microscopy and Auger electron spectroscopy were carried out for a variety of substrate bias voltages.Films deposited by hollow cathode discharge at 190°C and biased at 0 V and ?50 V and an electrochemically plated hard chromium film were compared by measurements of the Vickers microhardness and the line broadening of the (222)Cr line of X-ray diffraction after vacuum annealing at several temperatures. The hardness is approximately proportional to the square root of the line broadening.All the deposited films show a similar relation between hardness and line broadening. The square root of the grain size of these films as observed by TEM is inversely proportional to the hardness. This relation supports an empirical equation obtained by Agarwal et al. who worked with vacuum-deposited NiCr films. The grain size of the films as observed by TEM is several times larger than that calculated from line broadening.     

KH550修饰Al_2O_3及其对PI/Al_2O_3薄膜性能的影响

通过调整KH550的含量对Al2O3粉体表面进行改性,并用红外光谱(FT-IR)和X射线衍射(XRD)对改性后的粉体进行表征,表征结果显示KH550成功的键合到Al2O3粉体表面。然后分别使用Al2O3以及改性Al2O3制备了一系列无机粉体含量为16%(质量分数)的PI复合薄膜,通过扫描电子显微镜(SEM)对复合薄膜的断面微观形貌进行表征,并对复合薄膜的力学性能和击穿场强进行测试。测试结果显示KH550的含量对无机粉体分散情况有较大影响。当KH550含量为2%(质量分数)时,PI/KH550-Al2O3复合薄膜的拉伸强度和断裂伸长率最优,分别为130 MPa,12%,与PI/Al2O3薄膜相比,拉伸强度和断裂伸长率分别提高了22.8%,44.5%,击穿场强与其相近。     

Structural, electrical and optical properties of ZnO:Al films deposited on flexible organic substrates for solar cell applications

Aluminum doped ZnO thin films (ZnO:Al) were deposited on glass and poly carbonate (PC) substrate by r.f. magnetron sputtering. In addition, the electrical, optical properties of the films prepared at various sputtering powers were investigated. The XRD measurements revealed that all of the obtained films were polycrystalline with the hexagonal structure and had a preferred orientation with the c-axis perpendicular to the substrate. The ZnO:Al films were increasingly dark gray colored as the sputter power increased, resulting in the loss of transmittance. High quality films with the resistivity as low as 9.7 × 10^− 4 Ω-cm and transmittance over 90% have been obtained by suitably controlling the r.f. power.     

Processing and microstructure of porous and dense PZT thick films on Al2O3

The processing of porous PZT thick-film ceramics on Al₂O₃ has been studied. The films were screen-printed from a thixotropic ink of PZT with a 58% solids content. The thick films were sintered between 1000 and 1150°C for 2 h. The sintered films show a 10 m thickness and an average pore diameter ranging from 1–2 m. The PZT forms a continuous skeleton that can be filled with the desired polymer. Dense and continuous PZT films were fabricated by screen-printing PZT ink on previously electroded Al₂O₃ substrates with Ag/Pd 70/30 paste. Densification of the PZT was obtained by sintering near the liquidus temperature of the Ag-Pd system.     

Microstructural and electrical properties of PbTIO3 screen-printed thick films

In this article we will study the structural and electrical properties of PbTiO₃ (PTO) screen-printed thick films. These properties can change with synthetic routes employed for synthesis of PTO. The ceramic powder has been synthesized by mechanical alloying and solid state route. This material crystallizes in the tetragonal system, with space group P4mm and unit cell dimensions a = b = 3.904, c = 4.152 Å, and Z = 1. From our results, it was observed that PTO obtained by mechanical alloying provides smaller crystallite size. The Rietveld refinement showed that the samples synthesized by mechanical alloying and solid state route crystallize in the tetragonal system but with different cell parameters. The Raman shifts of these films agree with modes from literature. However, some displacements happen, because the morphology and structural characteristics of the thick films are different, compared to single crystal and thin film. The photomicrographs of the PTO thick films showed that the choice of synthetic routes obtained samples with different microstructures.     

Structural and electrical properties of Al doped ZnO thin films deposited at room temperature on poly(vinilidene fluoride) substrates

Transparent, conducting, Al-doped ZnO films have been deposited, by dc and pulsed dc magnetron sputtering, on glass and electroactive polymer (poly(vinylidene fluoride)–PVDF) substrates. Samples have been prepared at room temperature varying the argon sputtering pressure, after optimizing other processing conditions. All ZnO:Al films are polycrystalline and preferentially oriented along the [002] axis. Electrical resistivity around 3.3 × 10^− 3 Ω cm and optical transmittance of ~ 85% at 550 nm have been obtained for AZOY films deposited on glass, while a resistivity of 1.7 × 10^− 2 Ω cm and transmittance of ~ 70% at 550 nm have been attained in similar coatings on PVDF. One of the main parameters affecting film resistivity seems to be the roughness of the substrate.     

Fe3O4缓冲层对CoFe2O4薄膜磁性能的影响

采用射频磁控溅射在基片Si（100）和Fe3O4（20nm）/Si（100）上制备了钴铁氧体（CoFe2O4）薄膜，制备的薄膜在空气气氛中进行300～1000℃的退火处理，采用XRD、VSM分析了薄膜的微结构以及磁性能。结果表明，制备的钴铁氧体薄膜均具有尖晶石结构，Fe3O4缓冲层薄膜促进了钴铁氧体薄膜的结晶，但降低了钴铁氧体薄膜的垂直各向异性和垂直于膜面方向的矫顽力，而钴铁氧体薄膜的磁化强度和矩形度得到了一定的提高。     

柔性衬底铝掺杂氧化锌透明导电膜的特性研究

室温下采用射频磁控溅射法在有机薄膜－聚丙烯己二酯（polypropylene adipate,PPA)衬底上制备出了ZnO:Al(AZO)透明导电膜。其它制备参数保持不变的条件下通过改变淀积时间得到厚度不同的薄膜，并对不同厚度AZO薄膜的结构特性、光学特性和电学特性进行了研究。